Focusing during video with oly omd

I am not a video expert but I like the video quality of my Olympus and the effectiveness of IS. I am not very happy about the focusing ability with moving subjects or camera. I noticed I can lock focus on a moving target but I can lose it quite suddenly even if target speed remains constant. I never had a focusing issue with a camcorder although IQ with the Oly is way better. Most forums stress the fact that autofocus on these cameras is inherently more difficult. But I get the impression that camcorders just have a huge DOF since their sensor is much small than m43. I wonder in this regard how large sensor camcorders can focus vs small sensor peers.

Can any of you confirm my impressions and make some comments? I am quite confused about this subject...